I'm in the same position. I have a a very large product file and can no longer open it without CATIA crashing. I have heard something about "design mode" that will help this but I'm not real sure on how to activate it. I found an check box under options to automate design mode but I'm not sure if it is active presently.
On another note, I'm not sure what it does but I activated a memory warning in the options and the file seems to be loading now.